Cavity resonator construction



Aug. 26, 1952 R. L. WATHEN 2,608,618

CAVITY RESONATOR CONSTRUCTION Filed Dec. 11, 1945 2 SHEETS-SHEET lINVENTOR ATTORNEY Aug. 26, 1952 R, WATHEN 2,608,613

CAVITY RESONATOR CONSTRUCTION Filed D80. ll, 1945 i 2 SHEETS-SHEET 2INVENTOR ROBERT W/QTHLN Patented Aug. 26, 1952 UNITED STATES PATENTOFFICE CAVITY RESONATOR CONSTRUCTION Robert L. Wathen, Hempstead, N. Y.,assignor to y The Sperry Corporation, a corporation of Dela- ApplicationDecember 11, 1945, Serial No. 634,303

8 Claims.

This invention relates to cavity resonators which arcuseful atultra-high-frequencies and, more particularly, to methods ofconstructing such cavity resonators.

In the construction of cavity resonators it is desirable. especially inelectron discharge devices, that the heat that is generated in theresonator be conducted in as efficient a manner as possible to theexterior of the resonator where it may then be dissipated into thesurroundings. In order to do this, it is advantageous not only to havethe mass of the resonator large, but also that theheat conduction in alldirections away from the cavity resonator be large. This prevents localheating from occurring and aids in maintaining all parts of the tube atsubstantially equal temperatures. Under these circumstances temperaturecom-pensation may be carried out intelligently and the problem offrequency stability of an electron discharge or other apparatusincorporating a cavity resonator may behandled with greater ease. I

Another desirable feature in the construction of cavity resonators wouldbe the ability to assemble such cavity resonators of diiferent sizes butof the same resonant frequency.

Still another desirable feature in the construction of cavity resonatorswould be a method whereby the resonators, regardless of the final sizeand powerratings, could be assembled quickly at any convenient time froma few types of premanufactured parts.

In addition to these desirable features, it. is necessary that theresonators themselves be so constructed that tuning and removal ofelectromagnetic energy be easily accomplished.

In cavity resonators, which are to be used in electron discharge tubesor similar devices, it is necessary that there be openings in theresonator vide a construction and method of manufacture of [cavityresonators in which the component parts may be manufactured as units andthe final resonator assembledat a later time. v

Another objectrof this invention is to provide 2 a convenientconstruction and method of manufacturing cavity resonators havin largemass and efficient heat conducting properties so as to maintain allparts of the resonator at as nearly an equal temperature as possible.

Still another object of this invention is to provide a novel andconvenient construction and method of manufacturing cavity resonatorswhich are to be used in electron discharge tubes In accordance with thepresent invention, there is provided a novel and improved method ofconstructing and construction for cavity resonators. This improvedmethod consists of the manufacture of laminations which have a volumeremoved from them which is similar to the desired cross section of thecavity resonator; for example, toroidal shape. The laminations arepreferably thin for ease in manufacture, but in many applications theymay he of substantial thickness. The surface of these laminations inmost applications is formed of copper or a similar metal of highelectrical conductivity. This can be accomplished by electroplating orevaporating metals of high conductivity on the formed laminations, ormanufacturin the laminations themselves from such materials. Thelaminations are stacked together so that the volumes which are removedfrom them form a cavity with conducting walls. semicircular end sectionswhich may have openings in the shape of semitoroids are placed at eachend of the stack of laminations to complete the cavity resonatorstructure. Theinner surface of these end sections is also copper or asimilar metal. 'By a suitable heat treatment thelaminationsand the endsections are consolidated so as'to make one unitary cavity resonatorstructure. Special ar-, rangements provide for the passage of electronsthrough the resonator. V a

The invention in another ofits aspects relates to novel features of theinstrumentalities de,'. scribed herein for achieving theprincipalobjects of the invention and to novel principles employed inthose instrumentalities whether or not these features and principles areused for the said principal objects or in the said field.

A further object of the invention is to provide improved apparatus andinstrumentalities embodying novel features and principles, adapted foruse in realizing the above objects and also are adapted for use in otherfields.

Gther objects of the invention will be more apparent from the followingdescription taken in connection with the accompanying drawings in whicha preferred form of the invention is shown.

In the drawings,

Fig. 1 is a longitudinal cross-sectional View of an electron dischargedevice incorporating an embodiment of this invention;

Fig. 1A is a cross-sectional view of the embodiment shown in Fig. 1taken along line AzA thereof;

Fig. 1B is a similar cross-sectional view taken along line BB in Figs. 1and 1A; 7

Fig. 2 is an oblique exploded view of the'cavity resonator shown in Fig.1;

Fig. 3 is a cross-sectional view of part of a cavity resonator structureincluding its tuning mechanism; and

Fig. 4 is an oblique exploded view of a resonator structureincorporating a pair of cavity resonators.

Fig. 1 shows a longitudinal cross-sectional view of a reflex type ofklystron, the operation of which is described with respect to Fig. 2 ofU. S.

Patent No. 2,250,511. In this embodiment of the invention asubstantially rectangular flat cathode I is heated by a long heater coill I, heating current being supplied through supporting heating leads l2,which terminate in lead-in caps l3 in cathode shell 2|. leads 14 whichterminate in lead-in caps l5.

' The electrons which are emitted by cathode ID pass up through theopenings in the walls of cavity resonator l6 and are reflected back by asubstantially flat reflector electrode ll. This reflector electrode I!is supported by rods l8, which also serve as leads to supply thereflector electrode II with suitable potential. The rods [8 terminate inreflector electrode lead-in caps is. The complete structure is enclosedin an evacuated chamber formed by reflector shell 25 and cathode shell2| which are Vacuously sealed to the cavity resonator H3. The heaterleads I2 and cathode leads [4 are insulated electrically from thecathode shell 2| by glass seals 22. In a similar manner, reflectorelectrode leads 58 are insulated electrically from the reflector shell26 by glass seals 23.

The cavity resonator 56 in the above embodiment is shown in greaterdetail in Fig. 2. In this type of structure, preferably thin laminations24 (sayfrom .05 to .10 inch) are used. These laminations 24 have volumes25 and 26 removed from them, in the shape of a narrow central opening 26and circular end openings 25, the complete openings 25, 26 being similarto the dumbbell cross-section in the conventional toroidalshaped cavityresonator such as shown in U. S. Patent No. 2,242,275. It should beunderstood that the complete opening 25, 25 could be of many othershapes, as desiredfor the resonator, since the resonator could be of anyshape according to the characteristics desired for the device employingthe resonator. Since the laminations 24 are preferably thin, aconvenientmethod of manufacturing would be by punching or stamping out thesevolumes 25 and 26. However, the invention is not concerned with themanner in which the laminations are fabricated. The volumes 25 and 26may be removed by milling or machining or the laminations 24 themselvesCathode IE! is supported by 4 might be cast with the volumes and 26already provided.

These thin laminations 24 are preferably made of copper or a similarmetal. However, it is quite possible that they may be made of differentmetal than copper, but in such a case their surface is preferably ofcopper of a similar conductive metal.' Thus, for example, they may beconstructed of steel or Invar and plated with copper or silver, or theymay be cast of iron and sputtered with a good conductor.

In assembly, these thin laminations 24 are separated from one another bypairs of spacers 21 and 25. When viewed in cross section, it is seenthat these spacers 21 and 28 also have volumes 29 and 30 removed fromthem. These volumes 28 and 30 correspond to only the circular portions25 of the opening in the thin laminations 24. There is no spacer betweenthe laminations 24 adjacent to the central volume 26 of laminations 24which connects the circular volumes 25.

The spacers 21 and 28 are preferably made in a fashion similar tolaminations 24. As in the case of the laminations 24, the essentialfeature in most applications is that the surface consists of a goodconductor. An exemplary method that suggests itself for the constructionof these spacers 2'! and 28 is the longitudinal drilling of a bar ofcopper. After the bar has a hole drilled through it, whose diameter isthat of the cylindrical opening 25 of the cavity resonator desired, itis cut into sections of suitable sizes for storing and later as anassembly. Another method that lends itself quite neatly to the massproduction of such pieces would be die casting. This would assureuniformity of pieces at a'minimum of cost. The thin laminations 24 andpairs of spacers 2'! and 28 are stacked alternately until a resonator 16of desired length is obtained. In order end sections could bemanufactured in any.

of several ways. One such way is by providing 1 two portions each havinghalf the desired thickness of the complete end section. Half thesemitoroidal volume 56 could be removed from each such portion.Thereafter, the two portions could be joined. This would result in asemicircular end section of the desired thickness with the semitoroidalvolume 56 removed. The two halves could be preliminarily consolidated toform a unitary end section 55 or they could be merely clamped togetherand consolidated in a later operation.

After stacking laminations 24, spacers 21 and 28, and end sections 55together, they are given a suitable heat treatment (i. e., soldering,brazing, etc), so that the component parts consolidate to form a unitarystructure. The resonator I6 thus formed can then be used in an electrondischarge tube such as shown in the embodiment in Fig. J

As is seen in Fig. 1A, because of the present novel structure, it ispossible to have a large unobstructed area 3| across which electrons mayflow formed by the separation between the pairs of spacers 2'! and 28.Since this construction permits only a minimum number of electrons whichare emitted by the cathode [0 to be intercepted as they pass thru thealternating electromagnetic field of the cavity resonator it allows theusable power or the electron discharge tube to beincreased. l i Thecavity resonator 16 thus formed has many of the features which areconsidered desirable in resonatorconstruction. It has been constructedof components which are themselves quite easy to manufacture. Theresulting resonator assembled from these premanufactured partshasaconsiderable mass surrounding the cavity res onator, such mass havinghigh heat conductivitywhichaids in maintaining all parts of the cavityresonatorat substantially equal temperatures. i As has been discussed,an electron beam of large cross-sectioncan be projected into thealternatin electromagnetic field of the cavity resonator. Since aminimumnumber of electrons in the beam are intercepted the usable powerof-the electron tubes usingthis construction is large. Furthermore,tubes of different amounts-of power butwith the same frequency could beassembled as desired merely by stacking a suflicient number oflaminations and spacers together until the correct cavity resonatordimensions are obtained, since the resonator frequency is determined bythe shape ofthe opening 25, 26 and not by the overall resonator length.Such a cavity resonator, used with a cathode and reflector plate orcomparable dimensions, would thus result, when assembled, in a reflexk-lystron of a power output predetermined by the number of laminationsused, and Ofcorrect frequency. Thus, by having stock cathodes andreflector plates of different sizes and laminations, spacers, and endsections as described, reflex klystrons could be assembled quickly andcon veniently having predetermined power outputs covering a large range,all such klystrons having thesame desired frequency. For differentfrequencies, different laminations, spacers and end: sections are used,but with the samecathodes and reflectors.

If it is desired to construct a cavity resonator which is not to be usedin electron discharge devices, the spacers 21 and 28 can be omitted. Inthis way, by stacking a sufiicient number of identical laminations 24and usin two end sections 55, it is possible to quickly and convenientlyassemble a cavity resonator from premanuiac-- tured units.

In order to remove electromagnetic energy from the "cavity resonator,coupling loops are used.. Such a coupling loop is constructed in one ofthe spacers 32, shown in Fig.2. The crosssection of such a spacer 32 isshown in Fig. 1A and in Fig. 1B. A small loop 33, which links themagnetic field in the cavity resonator I6, is constructed within thespacer 32. This loop 33 terminatesin a coaxial line 34 sealed into therear of spacer 32. vacuum system, the coaxial line glass-t'o-metal seal35.

Tuning cavity resonators made in accordance 34 includes a 'witht'hisinvention may be accomplished in a rod 36' is shaped so that a portionofit forms a continuation of theirmer circular portion of the since theresonator is part of a 6 cross-section of the cavity "resonator 16. Asrod 36 is rotated about its axis 38 by knobil, shown in Fig. 1A, thecross-section of the reednator IS-is changed. The resulting fielddisturbancescause a change in resonant frequency.- Knob 39 is sealed to acylinder which in turn is sealed to the resonator cavity, to maintainthe vacuum envelope. If the tuning mechanism is to be used merely asatri'mmer in adjusting the resonant frequency of the cavity resonatoriiover small amounts, and quite infrequently, the

walls of'the cylinder 60 may be made of a ductile metal. However, if thetuningmechanismisto be used'r'epeatedly and-over large ranges, it ispreferable that the walls of the cylinder be of resilient metal. In sucha case, it is necessary to provide some sort of a locking fixture to thetuning'mechanism, such as a lock nut 6| which moves on threads 62provided on the outside walls of cylinder to. against the face 63 of theend section and maintains the rod 36 in the proper angular post tionafter it is turned by knob 39.

Another method of tuning that may be use'din a resonator constructedaccording to this inverttion is shown in Fig. 3, which is across-section of one of the spacers 28. In this method or tuning; ametal bar 40 which extends the length of the" resonator Hi is supportedina recess *whltih is in addition to the removed voluni'e3ll of thespacer 2B and the removed volume 25 of the thin lamination 24. Theinside face 42 of the metal bar 46 ordinarily forms a smoothcontinuation of the resonator wall. By the use of a rod orrods 43 whichpass through a vacuum seal' 44 of the bellows type, the metal bar 40 maybe moved sideways into the resonator I6, distortingth field therein andcausing a change in the resonant frequency.

Although the embodiment of the present iiivention described above usesbut a single cavity resonator, it is quite possible to construct multiple resonators in the same manner. Fig.4 shows an oblique explodedview of parts for a two-resonator structure. The thin laminations 45have twovolumes 46 and 41 removedfrohi them. These volumes 46 and 41 aresimilar to volumes 26 and 25 of the thin lamination- 14" shown in Fig.2'. Pairs of spacers 48 and 45 have tions 50 and 5| of the spacers 48and 49,. and the portions 53 i and 54 of the end section 52, are Ispaced from one another insuch a manner so ac to provide a drift spaceof the proper dimensions to allow for proper bunching. of theelectronsas they pass up through the space betweenspacers 48 and 43. Ifinternal coupling between the two resonators is desired, one or more ofthe laminations 45 may have a further opening 10' joining the circularopenings 41, 46.

Thus, the manner of manufacture and assent bly of a double resonator isthe same as that of a single resonator. The component parts, whosesurfaces in most applications are good conductoiui',v are consolidatedby proper heat treatment and the resulting structure is a double cavityreso' nator formed of premanufactured parts. Methods of tuning andcoupling of electromagnetic energy used in the single cavityresonatormay This locking nut 6i shoulders easilybe applied to such a, doublecavity reson r. l

;-Thus it can be seen that in accordancewith this invention, a cavityresonator may becon: structed using premanufactured elements and having:any desired length, corresponding to a predetermined power capacity. Themass sur: rounding the cavity resonator would be of sufiiciently highconductivity to allowthe heat which is, generated in the resonator to bequickly conductedtothe exterior, keeping all parts ofthe resonator atsubstantially equal temperatures. Thus temperature compensation caneasily be accomplished with the resultant increase in frequencystability. Furthermore, cavity resonators constructed according to thisinvention provide means whereby beams of electrons of large crosssectioncan be projected into the alternating electromagnetic field ofthe cavityresonator with a minimum number of such electrons beingintercepted bythe cavity resonator itself, thereby increasing the usable power. Y

Since many changes could be madein the above construction and manyapparently widely difierentembodiments of this invention could be madewithout departing from the scope thereof, it is intendedthat all mattercontained in the above description or shown in the accompanying drawings shall "be interpreted as illustrative and not in a limiting sense. I

v What is claimed is: L A unitary cavity resonator for supportingelectromagnetic oscillations formed of a plurality of thinconductive-surface,laminations having a relatively long dimension, aplurality of relatively said laminations, and a pair ofconductive-surface end sections, each of said laminations and endsections having corresponding openings therein, each of said spacershaving an opening therein which corresponds to at least part of theopening in saidv laminations ,andend sections, pairsof said spacersbeing disposed between successively spaced laminations, each pair ofsaid spacers comprising one spacer between adjacent ends: of twolaminations and the other spacer between the other endsof said twolaminations, said openingsin said spacers being in register with thecorresponding part of said openings in said laminations. and formingcontinuous passages therewith, said successively spacedlaminations andsaid pair of spacers therebetween'defining gaps surrounded at leastsubstantially by said passages;- said laminations and s'pacers'and endsections being consolidated to forms, unitary structure in which saidopenings and said passages define a smooth-walledunitary cavity withconductive walls, said unitary cavity being r850 nant at a predeterminedfrequency for electromagnetic oscillations i 2.- A unitary cavityresonator structure adapted to contain ultra high frequencyelectromagnetic oscillations, said structure being formed of a pluralityof conductive-surface laminations, a plurality of conductive-surfacespacers and a pair of conductive-surface end sections, each of saidlaminations and end sections having corresponding openings therein, eachof said spacers having an opening therein which corresponds to at leastpart of the said openings of said laminations and end sections, saidlaminations, spacers and and sections being consolidated toform aunitary structure in which said openings define a unitary cavity withconductive walls, said laminations consolidated in said unitarystructure defininga plurality of regularly spaced passages parallel tosaid laminations and transverse the unitary cavityfor' the passage of anI electronstream transverse the, cavity, said unitary cavity beingresonant at a predetermined frequency; 7

3..A, unitary r nu1tiple resonator structure adapted, to containultrahigh frequency electromagnetic oscillations, said structure being formedof a plurality of conductive-surface laminations, a plurality otconductive-surface spacers and a pair of conductive-surface endsections, each of said laminations having a plurality of separateopenings therein, each of said end sections having a similar pluralityof separate openings therein which correspond to said first separateopenings, each of said spacershaving a plurality of separate openingstherein which correspond to at least part of said openings, of saidlaminations and endsections, said laminations, spacers and end sectionsbeing consolidated to form a unitary structure in which said openingsdefine a plurality of cavities of a fixedand predetermined separation,open spaces being provided at regular intervals between successivespaced portions of said laminations in said structure whereby multipleparallel passages extend transverse said cavities through which anelectron stream mayv pass to provide tandem interactions with said,cavities, each of said cavities being-resonant at a predeterminedfrequency. 4. A unitary cavity resonator structure adapted to containultra high frequency electromagnetic oscillations, said structure beingformed of a plurality, of conductive-surface .laminations, a pluralityof conductive-surface spacers and, a pairlof conductive-surfaceendsections, eachoi saidlaminations and end sectionshavlng Corre--sponding openings therein, each of said spacers having an openingtherein corresponding to at least part of said laminations and endsections, one or more of said spacers having a coaxial line sealed toit, one end of said coaxial line terminating in a coupling .100p locatedinside of removed portions ;of said spacers, said laminations, spacersand end sections, being consolidated to form a unitary structure inwhich said .removed portions define a unitary cavity with conductingwalls and resonant at a predetermined frequency, said unitary structureincluding plural parallel passages therethrough along lines'surroundedby said-conducting walls of said unitary cavity, each passage beingbounded on two sides by parallel surfaces of successive laminations andbeing bounded at its two ends by the inner ends of a pair of spacersbetween the successive laminations defining the-passage. 5. A unitarycavity resonator structure adaptedto contain ultra high frequencyelectromagnetic oscillations, saidstructure being formed .of a pluralityof conductive-surface laminations and a pair of conductive-surface endsections, each of said laminations and end sections having correspondingopenings therein, .said laminations and end sections being. consolidatedto form a unitary cavity with conducting walls and res o-. nant'at apredetermined frequency,a tuning rod ofnoncircular' cross-sectionextending through said openings and perpendicular to said lamina,-tions, and'means for imparting rotationa1 dis-' placements tosai'd'rodiabout its longitudinal axis,

whereby said resonant, frequency is correspond oscillations, saidstructure being formed of a plurality of conductive-surface laminations,a plurality of conductive-surface spacers, and a pair ofconductive-surface end sections, each of said laminations, spacers andend sections having corresponding openings therein, said laminations,spacers and end sections being consolidated to form a unitary structurein which said openings define a unitary cavity with conductive walls andresonant at a predetermined frequency, said unitary cavity having atleast one straight portion of appreciable length extending transverselythrough a multiplicity of said laminations, a tuning rod extending anappreciable distance along said straight portion of said cavity. the

longitudinal axis of said rod being parallel to said straight cavityportion and perpendicular to said laminations, and means for varying theless tubular cavity being open to define an endless narrow gaptherealong, and a plurality of spaced cross-members extendingtransversely between said parallel passages and each having a slotextending therealong interconnecting said parallel passages at thenarrow gap thereat,

whereby the spaces between successive crossmembers define electronpermeable electrode 10 structure surrounded by said endless tubularcavity.

8. Electron discharge tube apparatus, comprising conductive means havingan endless tubular cavity, said tubular cavity comprising two oppositelydisposed and parallel tubular passages, and two curved tubular endsection passages, the innermost circumferential surface portion of saidendless tubular cavity being open to define an endless narrow gaptherealong, and a plurality of REFERENCES CITED The following referencesare of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,990 Hansen Mar. 23, 19482,352,190 Foote June 27, 1944 2,418,469 Hagstrum Apr. 8, 1947 2,433,368Johnson Dec. 30, 1947 2,440,851 Donal May 4, 1948 2,445,771 Fremlin July27, 1948 2,450,023

Spencer Sept. 28, 1948

